Mieke Bus

6 97 Endoluminal Ultrasound in the upper urinary tract Visualizing the mucosal layer, consisting of sub-layers of urothelium and lamina propria, is possible with ELUS. However, differentiation of these sub-layers is impossible due to a lack of contrast and low resolution. The 20mm imaging depth allows estimation of tumor size, although clear differentiation between non-invasive and invasive tumors cannot be achieved as a result of the limited resolution of ~100µm. Nonetheless, it is the deeper pene- tration depth of ELUS that makes this technique interesting for endourological applications. For example, an advantage of larger imaging depth is the ability to determine the relation of specific pathology with its direct surroundings, like lymphadenopathy in malignancy. (17) Advances of ELUS have led to small catheter-based ultrasound probes allowing visualiza- tion of a variety of luminal structures. (18) In the ureter, ELUS is mainly used in the diagnostic work-up of stenosis of the ureteropelvic junction (UPJ) and its relation with intersecting vessels. However a wide pathologic variety can be seen in the ureter, like upper urinary tract tumors and endometriosis. (17, 19, 20) ELUS is based on the detection of the time delay in high frequency sound waves, which are backscattered by tissue structures. The difference in resolution between OCT and ELUS is explained by the different wavelengths at which they operate. Unlike light waves in OCT, the transmission of sound waves needs a conduction medium, which is provided by the fluid present in the upper urinary tract lumen. A disadvantage of ELUS is the time needed for data acquisition, which is a factor 20 times longer compared to data acquisition using OCT. This increased acquisition time makes ELUS more sensitive to movements, resulting in blurred images. In an in-vivo setting, motion artefacts will occur due to ureteric peristalsis, breathing and movement at the point where the ureter intersects with the great vessels. A second limitation of ELUS is its sensitivity for air bubbles. This study shows data of OCT and ELUS acquired from the renal pelvis and ureter. Maneuvering the probe towards a suspected lesion in the renal pelvis compared to the ureter is more challenging but achievable after training of handling the imaging probe. Application of OCT and ELUS in the renal pelvis has been shown in previous studies as well. (4, 12, 20) CT as a guide for probe localization The main challenge in co-registration of endoluminal imaging techniques, is comparative localization with respect to histopathology. Co-registered ELUS and OCT combines greater depth imaging with superficial high-resolution images. To proof this, accurate correlation with histopathology is needed. To ensure that histopathology was obtained from the same location as OCT and ELUS measurements, accurate knowledge of probe position is needed. Therefore, we used CT to obtain reliable information on the intra-ureteral probe position, correlated to overall anatomy.